Experimental study on the fire behaviour of fibre reinforced concrete used in tunnel applications

Abstract

Guaranteeing the integrity of tunnel structures during and after fire is key in support of a sound fire safety strategy and for minimizing the risk of disruption in the operation of the tunnel due to restauration works post-fire. Innovations in concrete technology have enabled what is known as Fibre Reinforced Concrete (FRC); where very small fibres are used to substitute traditional reinforcement inside concrete. Within the scope of this study, the fire behaviour of a specific type of FRC including a combined dose of macro and micro polypropylene (PP) fibres is studied in depth. Experimental investigations were performed to study (1) the occurrence of fire-induced concrete spalling and (2) the integrity of macro PP fibres after cooling. Fire tests were performed using an H-TRIS test method set to condition concrete test samples to have an in-depth temperature gradient equivalent to that modelled for identical concrete under the Hydrocarbon curve in a standard furnace. Test results show that the time-to-spalling was directly influenced by the presence of macro and micro PP fibres; spalling happened earlier for concrete samples containing PP fibres. This study showed that macro PP fibres remained intact after cooling for depths where concrete was below the 300 °C threshold.